Laboratory X-ray micro-tomography system with crystallographic grain orientation mapping capabilities

ABSTRACT

A method and system for three dimensional crystallographic grain orientation mapping illuminates a polycrystalline sample with a broadband x-ray beam derived from a laboratory x-ray source, detects, on one or more x-ray detectors, diffracted beams from the sample, and processes data from said diffracted beams with the sample in different rotation positions to generate three dimensional reconstructions of grain orientation, position, and/or 3-D volume. A specific, cone beam, geometry leverages the fact that for a point x-ray source with a divergent beam on reflection of an extended crystal grain diffracts x-rays such that they are focused in the diffraction plane direction.

RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.14/057,126, filed on Oct. 18, 2013, which application claims the benefitunder 35 USC 119(e) of U.S. Provisional Application No. 61/715,696,filed on Oct. 18, 2012, both of which are incorporated herein byreference in their entirety.

BACKGROUND OF THE INVENTION

Metals, ceramics and other important materials are composed of manyindividual single crystal grains. For homogenous composition materials,the crystal structure of all grains is identical, but their relativecrystal orientation is not identical throughout the material. In factmany important engineering properties of materials are a function of thegrain properties, such as grain size, boundaries, size distribution, andorientation, to list a few examples.

Single composition poly-crystalline materials typically have no contrastto identify individual grains and boundaries in conventional x-raytomography scans based on absorption and/or phase contrast.

Electron backscatter diffraction imaging (EBSD) can be performed on thesurface of polished cross-sections of materials in a scanning electronmicroscope to image grains and grain boundaries in two dimensions. Thecrystal orientation of grains is determined in EBSD. Serial sectioningwith a focused ion beam milling tool and EBSD imaging can yield threedimensional (3-D) EBSD data. 3-D EBSD is a destructive measurementtechnique since the sample gets destroyed in the process, however.

Material evolution in the time domain as a function of external factorssuch as temperature cycling, stress or strain are extremely important tounderstand material failure and best processing conditions to yieldmaterials with optimum properties. Since 3-D EBSD can only capture thegrain map of a sample once, it is very unsatisfactory to study materialevolution.

X-ray diffraction contrast tomography (x-ray DCT) is a non-destructiveapproach for obtaining the 3-dimensional characterization ofpolycrystalline microstructures. It allows the simultaneous mapping ofthe crystal grain shapes, grain orientation and microstructure ofpolycrystals that gives rise to absorption.

In the conventional x-ray DCT arrangement, the sample is illuminatedwith a monochromatic beam of high energy synchrotron radiation. As thesample is rotated, and grains pass through the illuminating beam, thecondition for Bragg diffraction gets fulfilled by individual grains,these diffraction spots are recorded on a 2D detector placed behind thesample. The diffraction geometry is used to assign spots to the grainsfrom which they arise, and to determine the crystallographicorientations of grains. The spots are used as projections of the grainsto reconstruct the respective grain shapes. The technique has beenapplied to several materials science investigations, for example in the3D characterization of grain boundary networks, and in-situ studies ofinter-granular stress corrosion cracking in some stainless steels. Othermaterials investigated by x-ray DCT have included aluminum alloy Al1050. Most importantly, it is now possible to perform routine 3-D grainmap measurements non-destructively, which enables repetitivemeasurements to study time evolution.

The necessity to use synchrotron sources to perform these measurementsis very limiting and a laboratory source diffraction CT system wouldclose this gap. It is well known that synchrotrons generate x-rays withorders of magnitude higher brightness than laboratory sources, and themethods for DCT developed for the synchrotron require high beambrightness, which manifests itself in high beam collimation andmonochromaticity.

Laboratory sources generally have very poor brightness compared tosynchrotrons since they emit a very wide bandwidth of x-ray wavelengthsin terms of Bremsstrahlung. Characteristic emission lines emitted inaddition to the Bremsstrahlung background are low in intensity comparedto total x-ray power emitted, and the use of a monochromator (crystalmonochromator or multilayer) further reduces the intensity when tryingto monochromatize the beam of a laboratory source.

Nevertheless, U.S. Patent Application Publication No. 2012/0008736A1, toLauridsen et al., published on Jan. 12, 2012, describes an x-ray DCTsystem that can use a laboratory source. This system mirrors theimplementation of a synchrotron DCT setup, in that it assumes the use ofa focused and monochromatic x-ray beam. Additionally a scheme usingnon-standard detectors is described to detect the diffracted signal.

SUMMARY OF THE INVENTION

A problem with proposed configurations for laboratory-source x-ray DCTsystems is that their performance should be low. Since they require afocused, monochromatic beam, the resulting x-ray flux from existinglaboratory x-ray sources should be too low, resulting in impracticallylong exposure times.

A need continues to exist, therefore, for methods and systems capable ofperforming x-ray DCT analysis in the laboratory. In particular, a needexists for techniques that make it possible to use x-ray DCT in researchand industrial facilities that do not have a synchrotron radiationsource. Also particularly needed are arrangements that utilize simpleand effective detection systems.

In general, according to one aspect, the invention features a method forthree dimensional crystallographic grain orientation mapping. In themethod, a rotating sample is illuminated by a broadband, cone x-ray beamderived from a laboratory x-ray source, to generate, on an x-raydetector, a diffracted beam image. Data from the image coupled withinformation regarding an angle of sample rotation are processed (e.g.,by a controller) to obtain three dimensional reconstructions of grainorientation and position.

According to another aspect, the invention features an apparatus forthree dimensional crystallographic grain orientation mapping. Theapparatus includes a laboratory x-ray source, one or more optional x-rayconditioning devices such as apertures for restricting the extent of thecone beam from the source, a stage for rotating the sample, a singledetection system, preferably a high resolution pixilated x-ray detector,for collecting diffraction data, and a controller for processing datareceived by the detector, coupled with information regarding an angle ofsample rotation, to generate three dimensional reconstructions of grainorientation and position.

Utilizing the apparatus and techniques described herein,crystallographic mapping using x-ray DCT principles can be performed inthe laboratory with one of the primary advantages of the present systembeing its compact size. Compared with the synchrotron x-ray sourcestypically needed in traditional x-ray DCT experiments, the laboratoryx-ray source used here is small, much less expensive, and allowsconstant access. Furthermore, in contrast to previous approaches, abroadband, unfocused (cone) x-ray beam is used that more efficientlyutilizes the x-rays produced by a standard laboratory source.

The above and other features of the invention including various detailsof construction and combinations of parts, and other advantages, willnow be more particularly described with reference to the accompanyingdrawings and pointed out in the claims. It will be understood that theparticular method and device embodying the invention are shown by way ofillustration and not as a limitation of the invention. The principlesand features of this invention may be employed in various and numerousembodiments without departing from the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, reference characters refer to the sameparts throughout the different views. The drawings are not necessarilyto scale; emphasis has instead been placed upon illustrating theprinciples of the invention. Of the drawings:

FIG. 1 is a schematic perspective view showing the Laue focal plane 50and the projection plane 52 that are generated when x-rays from abroadband source illuminate one grain of a crystalline sample through anaperture;

FIG. 2A is a side view showing the relevant distances in the set-up ofFIG. 1;

FIG. 2B is a top view showing the relevant distances in the set-up ofFIG. 1;

FIG. 3A illustrates the image generated at the Laue focal plane andrelationship between the direct beam and the diffracted beam;

FIG. 3B illustrates the image generated at the projection plane and therelationship between the direct beam in the diffracted beam; and

FIG. 4 is a schematic diagram showing an x-ray and detector system of anapparatus that can be used to conduct x-ray DCT according to principlesof the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The current embodiment generally relates to a method and apparatus forobtaining three dimensional crystallographic grain orientation mapping.In contrast to previously described approaches, the system, andcorresponding method, uses a laboratory x-ray source and a detectionsystem, which is able to detect the x-rays transmitted through anddiffracted by the sample at preferably at least two distances from thesample in a conebeam geometry. Preferably, a high resolution pixilatedx-ray detector is used to collect diffracted x-rays and generatediffraction data. A lower resolution detector is used to detect thediffracted x-rays and projection images through the sample in theprojection plane.

During operation, the sample being studied is rotated utilizing, forinstance, a motion stage system with an angle of rotation (A), toproduce a series of angular projections. A controller receives imagedata of multiple images from the detection system (obtained whilerotating the sample) and performs three dimensional reconstructions ofgrain orientation and position.

Preferably, the system uses a “white” or broadband beam of x-rayradiation, i.e., a beam with a wide wavelength spectrum. The bandwidthof the x-ray beam is only restricted by the operating voltage of thex-ray source and optional absorption filters in the beam.

It is well known that a broadband (white) x-ray beam gives rise todiffraction patterns. For a single crystal/grain, this is referred toLaue diffraction patterns. Diffraction reflections manifest themselvesat specific angles corresponding to 1) the d-spacing of the crystalplanes, 2) the orientation of the planes and 3) one specific x-rayenergy or narrow range of x-ray energy that is selected from theincoming broad-band x-ray spectrum to fulfill the Bragg condition forreflection.

In polychromatic diffraction, each reflection off the crystal “selects”a specific wavelength or narrowband from the incident wavelengthspectrum. Generally many reflections of one crystal grain are present ina single diffraction pattern corresponding to various crystal planed-spacings, diffraction angles and x-ray wavelengths obeying the Braggcondition 2d*sin(β)=lambda, (or: 2d·sin β=λ), where d is the latticespacing, beta (β) the diffraction angle and lambda (λ) the wavelength.

For a single crystal material, a system controller analyzes thesediffraction patterns and the images detected by the detector system andextracts crystal orientation and lattice spacing from the data.

In a polycrystalline material that has many grains illuminated by thex-ray beam, each grain will contribute many reflections to thediffraction patterns. The polychromatic diffraction pattern of apolycrystalline sample using a collimated (parallel) incident x-ray beamin general leads to a superposition of many diffraction spots for whichit is not possible to decipher crystal grain association, wavelength andd-spacing. In fact, if a large number of grains are present, the randomorientation of the individual grains will give rise to so called Lauediffraction rings, which are well known in a diffraction method calledpowder diffraction. Powder diffraction is an established method todetermine the crystal structure of a material, but does not reveal anyspecific grain information.

In contrast, the present system uses a specific (cone beam) geometrythat leverages the fact that for a point x-ray source with a divergentbeam on reflection of an extended crystal grain diffracts x-rays suchthat they are focused in the diffraction plane direction to a distanceequal to the source-sample distance dss. We call this special plane theLaue focusing plane. This focusing effect is caused by the singlecrystal grain “seeing” the x-ray source under different incidence anglesover the extent of the crystal grain, which then selects differentwavelengths and diffraction angles for the reflection according to theaforementioned Bragg's law.

Different from collimated (parallel) beam polychromatic diffraction, thewavelength of the reflected x-rays is not constant across one grain inthe present system, but varies dependent on the position within thegrain where the x-rays strike.

FIG. 1 illustrates the Laue focal plane 50 and the projection plane 52.

In more detail, a broadband source 110 emits a diverging beam ofbroadband radiation 115. This radiation is diffracted by a crystal orgrain within the sample 10.

The diffraction effect by the crystal 10 yields the Laue focal plane 50where the x-rays that meet the Bragg condition are focused by thediffraction in the crystal or grain 10 of the sample. Since the focusingonly occurs in the diffraction plane, in general the pattern of thediffracted beam will form a line in the Laue focal plane. It is alsonoted that the distances between source and sample (dss) and betweensample and the Laue focal plane (dsd1) are equal. Then, at a furtherdistance from the sample 10, the projection plane 52 is found from theprojection of the diffracting crystal or grain. The distance of theprojection plane from the Laue focal plane is arbitrary and depends onthe pixel size of the x-ray detector available to record the pattern inthe projection plane.

FIG. 2A is a top view showing the relevant distances when a broadbanddiverging beam is diffracted by a sample crystal grain. Specifically,the distance between the source 110 and the sample 10 is dss. Thedistance between the sample 10 and the Laue focal plane 50 is dsd1 andthe distance between the sample 10 and the projection plane 52 is dsd2.

Of interest is the fact that different wavelengths or energies withinthe x-ray beam 115 meet the Bragg condition along different portions ofthe sample crystal or grain 10. Thus, the features generated at the Lauefocal plane 50 are combination of multiple wavelengths, λ1, λ2, λ3.These wavelengths are within the spectral band λmin to λmax containedwithin the broadband x-rays emitted by the source 110.

An aperture 112 is used between the source 110 and the sample 10 torestrict the illumination beam on the sample and separate the directtransmitted beam/non-diffracted beam 62, from the diffracted beam 60,64.

Since the diffracted beam 60, 64 is focused in the Laue plane, theprojected image of the crystal in the projection plane is inverted andhas a geometrical magnification that is given by (dsd2−dss)/dss, and canalso appear sheared.

FIG. 2B is a top view showing the relevant distances when a broadbanddiverging beam is diffracted by a sample crystal grain. The focusingeffect at the Laue focal plane 50 leads to the formation of line-shapedspots.

The appearance of the diffracted signals as line-shaped spots in theLaue focal plane comes from a focusing effect and a magnificationeffect. One such line shaped spot originates from the diffraction ofX-rays off one set of planes within one crystal grain of the sample. Thecrystal planes within the grain diffract and focus the X-rays alongtheir normal direction to a narrow line. This focusing effect occursacross the whole length of the crystal grain, which means that thelength of the line shaped spot in the Laue focal plane is a projectedrepresentation of the diffracting grain's physical size in thisdirection magnified by a factor of (dss+dsd1)/dss, which is equal to 2.The grain is projected non-inverted in this direction. From this itbecomes clear that in order to be able to resolve crystal dimensions inthe Laue focal plane a high-resolution detector will be required, whichis able to resolve the grain dimensions since the geometricmagnification is very low and equal to two. The magnification of theprojection of the grain in the projection plane is given by(dss+dsd2)/dss which is identical to projection x-ray imaging systems.The larger geometrical magnification in the projection plane enables theuse of lower resolution x-ray detector systems.

For example, as illustrated in FIG. 3A, a spatially resolved x-raydetector 150 located at the Laue focal plane 50 detects the lines 60that encode the orientation of the plane of the reflection. The lines 60at the Laue focal plane 50 are adjacent to any x-rays that form thedirect beam 62 that are not diffracted by the sample 10.

As illustrated in FIG. 3B, a spatially resolved x-ray detector 152located at the projection plane 52 detects reflected x-rays 64 onto aprojection plane detector 152 that give rise to a projection of thediffracting grain.

In the projection plane, the magnification of the projection of thegrain is not equal in the diffraction and orthogonal plane. In thediffraction plane the projection is inverted and has a lowermagnification than in the orthogonal plane. In the orthogonal plane, theprojection is non-inverted.

One strategy to obtain a re-projection of the grain outline into thesample plane for the reconstruction of a 3-D grain map is to re-projectthe grain shape from the projection plane through the line focus in theLaue focal plane 52. This allows for the identification of the index andwavelength giving rise to the reflection, knowing the geometry of thesetup (source position) along with inferences as to the exact grainlocation within the sample.

The identification of Friedel pairs in the diffraction data aids in theidentification of diffraction signals belonging to the same grain.

Shown in FIG. 4 is one example of an apparatus for conducting x-raythree dimensional crystallographic grain orientation mapping accordingto embodiments of the invention. The apparatus generally includes thex-ray source 110, for illuminating sample 10.

The source 110 is a “laboratory x-ray source”. It is preferably locatedon a source z-axis stage that enables independent adjustment of sourceto sample distance (dss). As used herein, a “laboratory x-ray source” isany suitable source of x-rays that is not a synchrotron x-ray radiationsource.

Source 110 can be an X-ray tube, in which electrons are accelerated in avacuum by an electric field and shot into a target piece of metal, withx-rays being emitted as the electrons decelerate in the metal.Typically, such sources produce a continuous spectrum of backgroundx-rays combined with sharp peaks in intensity at certain energies thatderive from the characteristic lines of the selected target, dependingon the type of metal target used. Furthermore, the x-ray beams aredivergent and lack spatial and temporal coherence.

In one example, source 110 is a rotating anode type or microfocusedsource, with a Tungsten target. Targets that include Molybdenum, Gold,Platinum, Silver or Copper also can be employed. Preferably atransmission configuration is used in which the electron beam strikesthe thin target 410 from its backside. The x-rays emitted from the otherside of the target are used as the beam 115.

In another, more specific example, source 110 is a structured anodex-ray source such as described in U.S. Pat. No. 7,443,953 issued to Yun,et al. on Oct. 28, 2008, the contents of which are incorporated hereinby reference in their entirety. In this case, the source has a thin toplayer made of the desired target material and a thicker bottom layermade of low atomic number and low density materials with good thermalproperties. The anode can include, for instance, a layer of copper withan optimal thickness deposited on a layer of beryllium or diamondsubstrate.

X-ray lasers producing radiation having an energy suitable for thetomographic applications described herein also can be employed.

In still another example, the source 110 is a metal jet x-ray sourcesuch as are available from Excillum AB, Kista, Sweden. This type ofsource uses microfocus tubes in which the anode is a liquid-metal jet.Thus, the anode is continuously regenerated and already molten.

The x-ray beam 115 generated by source 110 is preferably conditioned tosuppress unwanted energies or wavelengths of radiation. For example,undesired wavelengths present in the beam are eliminated or attenuated,using, for instance, an energy filter 412 (designed to select a desiredx-ray wavelength range (bandwidth)). Nevertheless, the filter 412 doesnot substantially reduce the total energy or bandwidth of thetransmitted beam 115. For example, the filter 412 preferably decreasesthe power in the beam by no greater than 50%. In the preferredembodiment, it decreases the power in the beam by no greater than 30%.The relevance is that most of the broadband x-rays generated by thex-ray source 110 are preserved to illuminate the sample 10. In generalthe bandwidth of the x-rays used are greater than 40% as defined by theratio of the central x-ray energy to the full width half maximum (FWHM)of the x-ray energy band. E.g. for a central energy of 50 keV an energyband of at least 20 keV around the central energy is used. In generalthe bandwidth is at least 20%, since otherwise the available flux of thesource is cut too severely. It is also recognized that by collectingdata with various x-ray source/filter combinations, the central energyand bandwidth are varied in some examples. This provides additionalinformation in the data that can be used by the control system 105 toidentify the wavelength range of recorded reflections.

The beam extent is preferably reduced by passing the x-ray beam throughaperture device 112, having a beam defining pinhole or appropriatesquare aperture. This aperture limits the illuminated region on thesample 10 and restricts the size of the direct beam on the x-raydetection system. It is recognized that by using different sizeapertures the number of crystal grains within the beam can be adjusted,which is advantageous to keep the number of diffraction reflectionsmanageable and reduce overlap of reflections. In general, every grainwill already have several reflections recorded in the Laue andprojection planes.

More than one energy filter 412 and/or aperture device 112 are employedin other implementations. On the other hand, this beam conditioning isomitted in cases in which the laboratory source (e.g., a laser)generates an adequately bandlimited and/or spatially limited beam.

The x-ray beam 115 derived (either directly, i.e., without furtherconditioning, for example in the case of a laser source, or conditionedas described above) from the laboratory x-ray source 110 illuminatessample 10, the sample being studied. Often, the sample 10 is apolycrystalline material having many crystal grains in which each grainconstitutes a crystal with translational symmetry. While the grains canhave the same chemical composition and lattice structure, they generallyhave different orientations.

Examples of materials that can be analyzed using the apparatus andtechniques described herein include but are not limited to metals, metalalloys, ceramics, and so forth.

The region of interest of the sample 10 is located in the beam using thex, y, z axis translatory capability of the sample stage 414. The sample10 is then rotated (see angle θ) around the y axis exposing differentsample faces to the incoming x-ray beam 115. In specific examples, thesample 110 is held in a sample holder mounted on a stage 414 (not shown)which allows rotation and, in preferred implementations, translation ofthe sample in relation to the x-ray beam 115 to allow for alignment.

For instance, the sample 10 can be manipulated using a conventionalsystem, which includes a sample holder and a stage system, ideallymotorized, for adjusting and rotating the sample 10. The stage 414 maybe designed for translation along (z-axis) and/or in the transversedirections (y and x axes) of the x-ray beam 115 illuminating the sample10, in the plane of the optical table (x-axis) and/or in a directionvertical to it (y-axis). For convenience, the coordinate system usedherein has as the z-axis the axis along optical path defined by theincoming x-ray beam; the x-axis as perpendicular to the incoming x-raybeam 115 (in the plane of the optical table); and the y-axis asprojecting in a direction perpendicular (vertical) with respect to the(horizontal) plane of the optical table.

In one example, the sample stage 414 is controlled by a systemcontroller 105 and has a central, rotational axis y and the position ofthe sample can be adjusted so that this rotational axis y isperpendicular to the direct path of the x-ray beam 115. The stage 414can rotate sample 10 about rotational axis y (see angle θ in FIG. 4)either with a predefined, settable rotational speed such as in the rangefrom 20 minutes to 24 hours per full rotation of 360° or in stepwise,incremental rotational movements that may be set such as in the rangefrom 0.01° to 15° per incremental rotation. The stage can have a defaultreference point for the rotational position of 0° and can provide anoption for setting an actual reference point at initiation of therotational movement of a mounted sample. The rotational angle of thestage with respect to the reference point is communicated from thesample staging device 414 to the system controller 105.

For instance, the sample 10 can be held on a sample holder, whichprojects from a base of the stage 414. The base can translate in the x-zplane under control of an x-z sample motion stage, allowing finepositioning of the sample on the plane of the optical table.

A sample rotation stage rotates the sample motion stage thus also thesample 10 in the x-ray beam 115, around an axis of rotation extendingparallel to the y-axis. An x-axis sample motion stage can be providedfor relatively large or gross positioning of the sample along thex-axis, allowing, for instance, the loading of the sample. A y-axis(translational) sample motion stage also can be provided for heightadjustments of the sample 10 in the x-ray beam 115 relative to the topof the optical table.

Interaction of the incoming x-ray beam with the rotating samplegenerates a series of angular projections 60 (see FIG. 3A) captured onthe scintillator 420 of the Laue plane x-ray detector 150. An x-ray stop418 is preferably provided to block or attenuate the direct beam fromthe x-ray source 110. The advantage of blocking the direct beam usingthe x-ray stop 418 is that the direct beam carries little informationabout the grain structure of the sample 10. Moreover, since its signalstrength is much stronger than any diffracted beam, blocking the directbeam improves the performance of the Laue plane x-ray detector 150 andreduces stray light generated in the scintillator 420. In general, thesize of the x-ray stop 418 is larger than the aperture 112 due to thediverging characteristic of the x-ray beam 115.

The x-ray stop 418 is selected to be partially transmissive to stillcollect an absorption contrast projection of the sample 10 on thescintillator 420 in some examples. This direct image is useful inreconstructing the outline of the sample and determining the center ofmass of the sample 10 by the controller 105.

In some implementations, a further filter 416 is located between thesample 10 and the scintillator 420. This can be used to filter out anyunwanted energies in the x-ray beam.

In either case, the incoming diffraction x-ray beam 60 and transmitted(or extinction) x-ray beam 62 (if not blocked) are converted by thescintillator 420 of the Laue plane x-ray detector 150 into photons oflower energy (typically within the visible range of the electromagneticspectrum). In turn, the lower energy (typically in the visible region)photon beams emitted from transmitted x-ray image 62, if present, andfrom the diffracted x-ray image 60 are further handled by an opticalportion 430 of the Laue plane x-ray detector 150.

The optical portion 430 of the Laue plane x-ray detector 150 typicallyincludes an optical magnification lens system and a detector, e.g., oneusing a suitable film or a camera detector based on a charge coupleddevice (CCD) or CMOS sensor. The image generated by the detector isprovided to the system controller 105.

The optical portion 430 is preferably optically disposed downstream fromscintillator 420. The optical portion 430 preferably includes amagnification lens held within a housing. Two couplets can be used tocondition the optical signal from the magnification lens. A final tubelens couplet forms images on the detector (e.g., a CCD camera).

In some examples, a turning mirror is included in the optical portion ofthe Laue plane x-ray detector 150. It is located prior to the lenses toavoid damage from the x-rays and allow any remaining x-rays to travel onto the subsequent projection plane x-ray detector 152. In the currentembodiment, the Laue detector 150 is removed to take images on theprojection plane detector 152. This is accomplished by the systemcontroller 105 switching out the detector 150 using a x or y-axis motionstage/switching system 422.

In general, suitable arrangements that can be used are described, forinstance, in U.S. Pat. No. 7,130,375 B1, issued to Yun et al. on Oct.13, 2006, the contents of which are incorporated herein by reference intheir entirety.

The Laue plane x-ray detector 150 is mounted utilizing the Z-axis motionstage/switching system 422 that further enables adjustment of theposition of the Laue plane x-ray detector 150 in the x, y and/or zdirections.

In specific examples, the source to sample distance dss (in the zdirection) is between 5 millimeters (mm) to 50 cm. The sample to Lauedetector distance dsd1 (also in the z direction) can be between 5 mm to50 cm.

In one configuration, the thickness of scintillator material 420 isbetween 50 μm and 1 millimeters (mm). It employs cesium iodide (CsI),cadmium tungstate (CdWO4) and so forth. The optical portion 430 thenprovides magnification of about 0.4× or more. In another implementation,thickness of scintillator is between 10 μm and 500 μm, with the opticalportion 430 providing a magnification of 4×. In a furtherimplementation, a thinner scintillator 420 of between 5 μm and 250 μm isused with the optical stage 430 providing a magnification of 10×. Athickness of 2 μm to 200 μm and an optical portion providing amagnification of 20× or more can be used as well. In yet other examples,the optical portion 430 provides for magnification of about 50× or less.

Interaction of the incoming x-ray beam with the rotating sample alsogenerates a series of angular projections 64 captured on thescintillator 432 of the projection plane x-ray detector 152. A secondx-ray stop 419 is preferably provided to block the direct beam from thex-ray source 110. Here again, the advantage of blocking the direct beamusing the x-ray stop 419 is that the direct beam carries littleinformation about the grain structure of the sample 10. Moreover, sinceits signal strength is much stronger than any diffracted beam, blockingthe direct beam improves the performance of the projection plane x-raydetector 152 and reduces stray light generated in the scintillator 432of the projection plane x-ray detector 152. In general, the size of thex-ray stop 419 is larger then the aperture 112 and the first x-ray stop418 due to the diverging characteristic of the x-ray beam 115. Howeverin other embodiments, the stop is 419 is attenuating, thus allowing thedetector 152 to also detect the direct beam.

A projection detector stage 424 supports and is used to position theprojection plane detector 152 along the beam axis 115.

In either case, the incoming diffraction x-ray beam 64 and transmitted(or extinction) x-ray beam 62 (if not blocked) are converted by thescintillator 432 of the projection plane x-ray detector 152 into photonsof lower energy (typically within the visible range of theelectromagnetic spectrum). In turn, the lower energy (typically in thevisible region) photon beams emitted from transmitted direct x-ray image62 and from diffracted x-ray image 64 are further handled by an opticalportion 434 of the projection plane x-ray detector.

The optical portion 434 of the projection plane x-ray detector 152 canbe much simpler than the Laue plane x-ray detector system 150. This isbecause, due to the geometrical magnification, the images are larger onthe projection plane detector 152.

In one example, no optical magnification is provided. Instead a CCDpanel detector is used directly after the scintillator 432. For example,a flat panel detector with 1:1 coupling to the scintillator 432 can beused. Such detectors have pixel sizes ranging typically from 50 μm to250 μm.

In another example, optical portion 434 of the projection plane detector152 has a visible light magnification of 0.4× and the CMOS sensor with apixel size of 13 μm.

In one simple example, the Laue plane detector 150 and the projectionplane detector 152 are the same physical detector. For each angle thetaof the sample 10 relative to the beam, the detector is moved between theLaue plane 50 and the projection plane 52. This configuration requires adetector stage 422 with a large translation capability in the z and xaxes.

In specific examples, the sample to projection detector distance dsd2(also in the z direction) can be between 10 cm to 100 cm. Thegeometrical magnification of the x-rays at the projection plane detector152 is preferably between 10 and 500.

The apparatus described herein also includes the system controller 105.The controller can be any processing unit suitable for carrying out theoperations needed in order to obtain three dimensional crystallographicgrain orientation mapping of the sample material. For instance, thecontroller 105 can be a computer system capable of receiving image dataof multiple images from the detector systems 150, 152 (taken whilerotating the sample 10) and for performing three dimensionalreconstructions of grain orientation and position. In specificimplementations, the controller 105 also controls the rotation stage 414and thus the angle of rotation of the sample 10 being examined.Preferably, also the controller 105 operates the stages 422, 424 of theLaue plane detector 150 and the projection plane detector 152. And,specifically, the controller 105 moves the Laue plane detector 150 outof the optical path to enable detection by the projection plane detector152, or moves the Laue plane detector 150 to the position of theprojection plane detector 152 to perform its function.

In some cases, the controller 105 uses only data from the Laue detector150 or only data from the projection plane data 152 to analyze thesample 10. In general, however, the information derived from the Lauedetector 150 is most helpful in the analysis of the sample.

In many aspects of the invention, the controller 105 utilizes principlesof x-ray DCT to generate a three dimensional crystallographic grainorientation mapping. Established DCT principles are described in severalpublications, all being incorporated herein by reference in theirentirety. These publications are: W. Ludwig et al., X-Ray DiffractionContrast Tomography: A Novel Technique For Three-Dimensional GrainMapping of Polycrystals. I. Direct Beam Case, J. Appl. Cryst. (2008)V41, pp. 302-309 (Appendix A); G. Johnson et al., X-Ray DiffractionContrast Tomography: A Novel Technique For Three-Dimensional GrainMapping of Polycrystals. II. The Combined Case, J. Appl. Cryst. (2008)V41, pp. 310-318 (Appendix B); Martin Knapi{hacek over (c)}, Seminar,4^(th) Year, University of Ljubliana, Facutly of Mathematics andPhysics, Physics Department, May 28, 2011 (Appendix C); and U.S. PatentApplication Publication No. 2012/0008736A1, to E. M. Lauridsen et al.,published on Jan. 12, 2012 (Appendix D).

As described in the literature (see, e.g., Ludwig, et al. (2008). J.Appl. Cryst. 41, 302-309) x-ray DCT has some similarities toconventional X-ray absorption contrast tomography. Typically, grains inthe sample are imaged using the occasionally occurring diffractioncontribution to the X-ray attenuation coefficient each time a grainfulfils the diffraction condition. The three-dimensional grain shapesare reconstructed from a limited number of projections using analgebraic reconstruction technique (ART). Algorithms based on scanningorientation space and aiming at determining the correspondingcrystallographic grain orientations also have been developed.

By simultaneous acquisition of the transmitted and the diffracted beams,the technique described by Ludwig, et al. (2008). J. Appl. Cryst. 41,302-309 has been extended (see, e.g., G. Johnson et al., J. Appl. Cryst.(2008) V41, pp. 310-318) to the study of underformed polycrystallinesamples containing more than 100 grains per cross section. Here, thegrains are still imaged using the occasionally occurring diffractioncontribution to the X-ray attenuation coefficient (which can be observedas a reduction in the intensity of the transmitted or direct beam 62when a grain fulfils the diffraction condition). The segmentation of theextinction spot images with the additional diffracted beam informationhas been automated even in the presence of significant spot overlap. Bypairing the corresponding direct (‘extinction’) and diffracted beamspots a robust sorting and indexing approach has been developed.

In general, with the present system, each grain in the sample 10produces typically multiple, 1-20, diffraction spots or lines on theLaue detector 150 at every angle of the sample 10 to the x-ray beam axis115. This effect can be used to eliminate the need for continuousrotation (theta) of the sample 10. Additionally, the line geometry ofthe diffraction spots in the Laue plane reduces the “overlap” problemsince the lines can be separated more easily than large spots, which aredetected with traditional systems.

In one embodiment, data from regions 60, 62, and 64 detected by the Lauedetector 150 and the projection plane detector 152 are communicated withthe controller 105. Besides receiving signals from transmitted image 62and diffraction spots 60, 64 from diffracted image, the controller 105preferably also controls the sample stage 414 so that the crystallinematerial sample 10 is automatically rotated during the exposure process.

While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

For example, use of a broadband x-ray spectrum for DCT has not beenconsidered at synchrotron radiation sources. If a synchrotron beam wouldbe conditioned to deliver a diverging broadband beam to apolycrystalline sample, the same methods as described above can beemployed potentially offering significant performance advantages overthe currently used methods, which use a monochromatic beam. In fact,underutilized, low-brightness bending magnet beamlines at synchrotronscould be used instead of a laboratory source to provide the broadband,divergent x-ray beam.

What is claimed is:
 1. A method for crystallographic grain orientationmapping, the method comprising: illuminating a polycrystalline samplewith a diverging x-ray beam derived from an x-ray source; detectingdiffracted beams from the sample; and using the detected diffractedbeams for the sample in different rotation positions to generate grainorientation information.
 2. The method of claim 1, further comprisingusing the detected diffracted beams with the sample in differentrotation positions to generate grain position and/or grain shape and/orgrain size information.
 3. The method of claim 1, further comprisingdetecting x-rays from the sample at least two distances from the sample.4. The method of claim 1, further comprising varying a bandwidth of thex-ray beam.
 5. The method of claim 1, further comprising varying acentral energy of the x-ray beam.
 6. The method of claim 1, wherein,before illuminating the sample, the x ray beam generated by the x-raysource is passed through an aperture that controls beam divergence. 7.The method of claim 1, wherein the one or more x-ray detectors comprisea high resolution pixilated x-ray detector to collect diffracted x-raysand generate diffraction data and a lower resolution detector to detectgrain projection images through the sample.
 8. The method of claim 1,further comprising detecting the diffracted beams at a Laue focal plane.9. The method of claim 1, further comprising generating the x-ray beamby irradiating a liquid metal target.
 10. The method of claim 1, furthercomprising generating the x-ray beam by irradiating an anode that iscontinuously regenerated.
 11. The method of claim 1, further comprisingconditioning the x-ray beam that illuminates the sample with a spectralfilter that reduces a total power in the beam by no greater than 50%.12. The method of claim 1, further comprising providing an x-ray stop toblock or attenuate a direct beam from the x-ray source from reaching anx-ray detector.
 13. The method of claim 1, further comprising collectingan absorption contrast projection of the sample and using a resultingdirect image to determine characteristics of the sample.
 14. The methodof claim 1, further comprising positioning a detector, which detects thediffracted beams from the sample, to detect the beams that have beenfocused by the sample.
 15. An apparatus for crystallographic grainorientation mapping, comprising: an x-ray source generating a divergingx-ray beam; a sample rotation stage for rotating the sample in the x-raybeam; at least one x-ray detector to collect diffraction data from thesample; and a controller for receiving the diffraction data from thedetector for different rotation positions of the sample and generatinggrain orientation information.
 16. The apparatus of claim 15, whereinthe controller uses the diffraction data to generate grain positionand/or grain shape and/or grain size information.
 17. The apparatus ofclaim 15, wherein the at least one x-ray detector detects x-rays fromthe sample at at least two distances from the sample.
 18. The apparatusof claim 15, further comprising varying a bandwidth of the x-ray beam.19. The apparatus of claim 15, further comprising varying a centralenergy of the x-ray beam.
 20. The apparatus of claim 15, furthercomprising a beam defining aperture for limiting an illuminated area onthe sample and restricting the size of a direct beam on the detector.21. The apparatus of claim 15, wherein the at least one x-ray detectorcomprises a high resolution pixilated x-ray detector to collectdiffracted x-rays and generate diffraction data and a lower resolutiondetector to detect projection images through the sample.
 22. Theapparatus of claim 15, wherein the at least one x-ray detector comprisesan x-ray detector at a Laue focal plane.
 23. The apparatus of claim 15,wherein the x-ray source has an anode that is continuously regenerated.24. The apparatus of claim 15, wherein the x-ray detector is positionedto detect diffracted beams from the sample that have been focused by thesample.